Keywords: tramcars, sharp curves, contact forces, independently rotating wheels.

Modern articulated tramcars are characterised by structural configurations and design solutions (e.g. low-floor cars, independently rotating wheels, resilient wheels, etc.) which can significantly differ from those of traditional rail vehicles. Moreover, the operating conditions in tramways show peculiar characteristics (sharp curves, grooved rails, etc.) which require specific investigation.In particular, when dealing with sharp curve negotiation, the analysis of the contact forces at the wheel-rail interface is of fundamental importance for all the key aspects of tramway operation including: safety, limitation of the wear rates in rail-wheel profiles, squeal noise mitigation. The purpose of this paper is to show how these contact forces change with variable bogie architecture.

All the analyses presented are based on vehicle multi-body simulations, carried out by means of a numerical model specifical for tramcars, which was developed at the Politecnico di Milano [1]. The numerical model was validated by comparing the simulation results with the experimental data collected during tests carried out both on-line and on a full-scale test-rig [2,3].

In the first part of the paper attention is focused on the steady-state behaviour in a curve, considering:

1. The full-curve distribution of the lateral contact forces on the four wheels within a bogie, for variable curve radius, in the case of solid axles and independently rotating wheels; the comparison between these two axle configurations enables the mechanisms which govern the forces exchanged at wheel-rail interface to be pointed out and also shows how the absence of the longitudinal contact forces in the case of independently rotating wheels leads to a completely different distribution of the lateral contact forces on the four wheels;
2. The effect of the possible occurrence of a contact between the flange-back of the leading axle inner wheel and the groove inner sidewall, as a consequence of the tolerances in the track gauge and of the deformability of the rubber elements of a resilient wheel.

The second part of the paper is devoted to the vehicle transient behaviour. The vehicle free response excited in correspondence with the sudden transition from a tangent to curved track at the curve entrance or exit and the vehicle forced response to the random input associated with track irregularity are considered.

1

P. Belforte, F. Cheli, R. Corradi, A. Facchinetti, "Software for the numerical simulation of tramcar vehicle dynamics", Heavy Vehicle Systems, 19(1-2), 48-69, 2003. doi:10.1504/IJHVS.2003.002434

2

F. Cheli, R. Corradi, G. Diana, A. Facchinetti, "Validation of a numerical model for the simulation of tramcar vehicle dynamics by means of comparison with experimental data", Journal of Computational and Nonlinear Dynamics, 2(4), 299-309, 2007. doi:10.1115/1.2754306

3

F. Cheli, R. Corradi, A. Facchinetti, L. Mazzola, "Prediction of running safety for a tramcar equipped with independently rotating wheels by means of numerical simulations and experimental tests", 7th International Conference on Railway Bogies and Running Gears (Bogie '07), Budapest, Hungary, 3-6 September 2007.

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